Test your skills of deduction with the February 2022 edition of Riddle Me This: A Spinning Disk
On a table in front of you is a spinning disk, much like a vinyl record on a turntable. One half of the disk’s surface is colored white, and the other half is colored black. The disk is spinning so fast that you are not able to tell which direction it is spinning. You also have an unlimited number of color sensors that will light up when the surface below them is black.
How many of these sensors would you have to place and where would you place them to determine which way the disk is spinning?
Click to Reveal Answer
Could you do it with one sensor moving tangentially back and forth, measuring the doppler shift? The flash rate would be slower when the sensor is moving in the direction of the spin, and faster when it is moving in the opposite direction of the spin. Just a thought…
Two, relatively next to each other (~1″ apart, radially close to the outer rim). This assumes that you would be able to interpret the sensors’ output any differently than you would be able to observe the disk with just visual acuity.
Hmm – this is tricky. It only says, “One half of the disk’s surface is colored white, and the other half is colored black.” It assumes that the disk is not one color on the inside and another on the outside. What if it’s a checkered pattern?
I think that Eric has the right idea.